09:15 〜 09:30
[MIS04-02] Effect of orbitally-driven insolation changes on East Asian monsoon rainfall over the past 450,000 years
キーワード：東アジア夏季モンスーン、日射量、氷床量、気候モデリング、大気-海洋相互作用
Understanding orbital-scale changes in East Asian summer monsoon (EASM) precipitation is one of the fundamental issues in paleoclimate research, for determining the response of East Asian monsoon to different climate forcings such as insolation, ice volume, and greenhouse gases. Proxy records suggest that East Asian summer monsoon precipitation over the last hundreds of thousands of years has fluctuated associated with orbitally driven insolation changes and/or changes in global ice volume. However, due to the inconsistency between different proxies, it has been controversial what was the essential driving force for the EASM variability.
In the present study, we aim to evaluate the effect of insolation changes on the EASM based on numerical simulations. Using a climate model (MRI-CGCM 3.2), the global climate under given insolation changes for the past 450,000 years were calculated. The results showed that the summer precipitation in East Asia varies at the periodicities of precession (23 kyr) and obliquity (41 kyr), consistently with insolation changes. The calculated temporal changes in summer precipitation is highly consistent with cave speleothem d18O data in South East China, while the proxy data from North China (Chinese Loess Plateau) and Japan (Lake Biwa) cannot be fully explained by the calculation results. Importantly, the 100-kyr periodicity which dominates the variation in Chinese Loess Plateau was not found in our calculation results. We found a strong positive correlation between insolation and precipitation over the coastal area of China and a negative correlation between insolation and precipitation around Japan, which implies that EASM intensity is strongly affected by insolation intensity and but the effect can vary between regions.
The positive correlation between boreal summer insolation and summer precipitation over China results from the atmosphere-ocean interaction over the Indian Ocean and the western Pacific. Under strong insolation, northern shift of a monsoon front associated with intensification of the North Pacific subtropical high causes the increase in rainfall in the coastal area of China. Intensification of the subtropical high is caused by the integration of local Wind-Evaporation-Sea Surface Temperature (WES) feedback with Kelvin wave response to the warm Indian Ocean (IPOC mode). On the other hand, the correlation between insolation and precipitation around Japan affected by the strength of North Pacific High. Under strong insolation, the North Pacific High intensified, which causes decrease in summer precipitation around Japan.
In the present study, we aim to evaluate the effect of insolation changes on the EASM based on numerical simulations. Using a climate model (MRI-CGCM 3.2), the global climate under given insolation changes for the past 450,000 years were calculated. The results showed that the summer precipitation in East Asia varies at the periodicities of precession (23 kyr) and obliquity (41 kyr), consistently with insolation changes. The calculated temporal changes in summer precipitation is highly consistent with cave speleothem d18O data in South East China, while the proxy data from North China (Chinese Loess Plateau) and Japan (Lake Biwa) cannot be fully explained by the calculation results. Importantly, the 100-kyr periodicity which dominates the variation in Chinese Loess Plateau was not found in our calculation results. We found a strong positive correlation between insolation and precipitation over the coastal area of China and a negative correlation between insolation and precipitation around Japan, which implies that EASM intensity is strongly affected by insolation intensity and but the effect can vary between regions.
The positive correlation between boreal summer insolation and summer precipitation over China results from the atmosphere-ocean interaction over the Indian Ocean and the western Pacific. Under strong insolation, northern shift of a monsoon front associated with intensification of the North Pacific subtropical high causes the increase in rainfall in the coastal area of China. Intensification of the subtropical high is caused by the integration of local Wind-Evaporation-Sea Surface Temperature (WES) feedback with Kelvin wave response to the warm Indian Ocean (IPOC mode). On the other hand, the correlation between insolation and precipitation around Japan affected by the strength of North Pacific High. Under strong insolation, the North Pacific High intensified, which causes decrease in summer precipitation around Japan.